This invention relates in general to vehicle wheels and in particular to a method and cutting tool for machining a portion of the vehicle wheel outboard face to produce a smooth surface and a process for chrome plating the smooth surface.
Vehicle wheels typically include an annular wheel rim and a circular wheel disc. The wheel disc can be formed across the outboard end of the wheel rim or recessed within the wheel rim. The wheel rim is adapted to carry a pneumatically inflated tire. The wheel rim has inboard and outboard tire retaining flanges formed on the ends thereof which extend in an outward radial direction to retain the tire on the wheel. Inboard and outboard tire bead seats are formed on the outer surface of the wheel rim adjacent to the corresponding tire retaining flange to support the tire wall beads and form an air-tight seal therewith. The wheel rim also includes a reduced diameter deep well between the tire bead seats to facilitate mounting the tire upon the wheel.
The wheel disc includes a central wheel hub for mounting the wheel upon a vehicle. The inboard face of the wheel disc hub is typically machined to form a flat surface to assure good contact between the wheel disc and the vehicle wheel hub. A pilot hole and a plurality of wheel stud holes extend through the wheel hub. The pilot hole is centered on the hub and the stud holes are spaced equally about a bolt hole circle which is concentric with the pilot hole. The pilot hole can receive the end of an axle while the wheel stud holes receive wheel studs for attaching the wheel to the vehicle. The wheel disc also typically includes a plurality of wheel spokes which extend radially from the wheel hub to the wheel rim and support the hub within the rim.
Referring now to the drawings, a flow chart for a wheel manufacturing process is shown in FIG. 1. In functional block 10, a wheel is cast in a single piece from a light weight metal such as aluminum, magnesium or titanium, or an alloy of a light weight metal. Such wheels are becoming increasingly popular because they weigh less than conventional steel wheels and can include outboard wheel disc faces which are formed in a pleasing aesthetic shape. One piece wheel castings are usually formed by a gravity or low pressure casting process. The wheel castings are finished by machining to a final shape.
Two separate machining stations are typically used to finish a wheel casting. In functional block 11, the outboard end of a rough wheel casting is clamped to the face of a first wheel lathe for a first set of machining operations. A wheel lathe is a dedicated machine designed to finish wheels. Wheel lathes typically include a plurality of cutting tools mounted upon a lathe turret. The turret is indexed to sequentially move each of the tools to the surface of the wheel casting. Wheel lathes are usually operated under Computer Numerical Control (CNC) to sequentially perform a number of related machining operations. For example, a wheel lathe turret can be equipped with a turning tool, a facing tool and a drill bit and the wheel lathe can be programmed to sequentially turn, face and bore a wheel casting. The wheel lathe face typically includes a chuck having a plurality of jaws which grip the outboard wheel retaining flange and tire bead seat. Consequently, the outboard wheel rim end is not finished during the first set of machining operations.
The outside and inside surfaces of the wheel rim are turned to their final shapes and the inboard surface of the wheel hub is faced in functional block 12. Additionally, the inboard end of the wheel rim is finished. The partially finished wheel casting is removed from the first wheel lathe, reversed and clamped on a second wheel lathe for a second set of machining operations in functional block 13. During the second set of machining operations, the inboard wheel flange and tire bead seat are gripped in the jaws of the wheel lathe chuck, exposing the outboard surface of the wheel disc and the outboard end of the wheel rim for machining.
In functional block 14, the second wheel lathe turns and faces the outboard wheel face. During these operations, the outboard tire retaining flange and the outboard tire bead seat also are turned to final shapes. The surface of the hubcap retention area is machined to final shape and the stud mounting holes are drilled through the hub in functional block 15. Alternately, the wheel casting may be removed from the wheel lathe and the drilling operation completed at another work station.
During the facing and other machining operations, very fine grooves are formed in the surfaces of the wheel. Accordingly, the surface of the wheel is typically subjected to a finishing step, as shown in functional block 16. A typical finishing process involves polishing the wheel surface to smooth the grooves and provide a lustrous appearance to the surface of the wheel. The polishing is usually followed by application of a clear coating to protect the polished wheel surface.
A typical polishing and chrome plating operation is illustrated by a flow chart in FIG. 2. Polishing typically involves a first step of rough buffing with an abrasive compound as shown in functional block 20. The buffed wheel is degreased in functional block 21. One frequently used method of degreasing involves passing the wheel through a chamber which is filled with a solvent vapor. The solvent vapor condenses upon wheel, covering the entire wheel surface. Once the solvent has had a sufficient time to dissolve any surface grease, the solvent is washed from the wheel to complete the degreasing. As shown in functional block 22, the wheel is then wet polished with a liquid lubricant for the polishing abrasive. The wheel is usually rotated and rotating polishing wheels are applied to the surface while a slurry of polishing abrasive and a carrier fluid is applied to the wheel surface. Next the wheel is rinsed in functional block 23. Typically, deionized water is used for the rinse.
The substances utilized during wheel polishing are generally toxic in nature. Accordingly, it is common practice to ship the wheels to a polishing contractor who employs safety procedures to protect personnel. The contractor is also equipped to dispose of the toxic wastes generated by the polishing operations.
The polished wheel surface is buffed in functional block 24. Typically, the buffing step utilizes a rag and buffing compound to create a surface smooth and shiny enough to achieve the generally accepted smoothness and clarity required for chrome plating an aluminum wheel. The wheel is now ready for the chrome plating process.
The chrome plating, which may be provided at the polishing facility, or after shipment of the wheel to an off-site chrome plating facility, consists of depositing a number of metal layers upon the surface of the polished wheel. Chrome plating involves the deposition of multiple metallic layers upon the wheel surface and begins in functional block 26, where a layer of copper 28 is chemically deposited upon the polished surface of a wheel 30, as illustrated in FIG. 4 by a fragmentary sectional view of a portion of a wheel surface. Typically, the portion of the wheel being plated is immersed in a chemical bath containing copper in solution. An electric current is passed though the copper solution and the wheel to attract the copper to the wheel surface where it chemically bonds to the wheel metal. The copper layer 28 is then buffed in functional block 32 to provide a smooth surface for deposition of the remaining layers.
The copper layer 28 is needed to form a barrier between the subsequently applied layers and the wheel surface. During casting of the wheel, a sealing layer is formed upon the wheel surface, such as, for example, aluminum oxide upon an aluminum cast wheel. However, when surfaces of the wheel of the wheel are machined, the sealing layer is removed, exposing surface pores that may absorb moisture. Over time, the trapped moisture may begin to oxidize the chromed surface from underneath. Additionally, as described above, the polishing process to prepare the wheel for plating uses polishing compounds that may be trapped within the surface pores and may begin to oxidize over time, which also would have an adverse effect upon the appearance of the plated surface. Therefore, the copper layer 28 is applied to form a barrier, or sealing layer, between the wheel surface and the subsequently applied layers.
Continuing to the next step shown in the flow chart of FIG. 2, a layer of semi-bright nickel 34 is chemically deposited over the copper layer 28 in functional block 36. The semi-bright nickel layer 34 provides additional corrosion resistance for the plated surface. Next, in functional block 38, a layer of bright nickel 40 is chemically deposited over the semi-bright nickel layer 34 to provide reflectivity and brightness to the wheel surface. Finally, in functional block 42 a layer of chromium 44 is chemically deposited over the bright nickel layer 34 to prevent nickel fogging. Typically, the nickel and chromium layers 34, 40 and 42 are formed by immersing the portion of the wheel being plated in a chemical bath containing a solution of the particular metal to be deposited upon the wheel surface. As described above, an electrical current is passed through the solution and the wheel to attract the metal to the wheel surface. Thus, each layer is chemically bonded to the preceding layer to provide a durable and attractive decorative surface coating on the wheel.